1. Field of the Invention
The present invention relates to a substrate for liquid crystal display and a liquid crystal display unit, and more particularly to a substrate for liquid crystal display used suitably for a MVA (multi-domain Vertical Alignment) type liquid crystal display and a liquid crystal display unit provided therewith.
2. Description of the Related Art
Since a liquid crystal display has advantages of compact, thin, a low consumption of electric power, and light-weight, it is widely used for a variety of electronics devices at present. Particularly, an active matrix type liquid crystal display containing switching devices is widely adopted for business machines such as a personal computer, audio-video equipment such as TV, cellular phone and the like. In such liquid crystal displays, improvements in quality levels such as growing in size, high-definition, increase in a ratio of pixel effective area (high aperture ratio), wide visual field, and increase in color purity develop rapidly in recent years.
A schematic structure of a liquid crystal display is such that a liquid crystal is sandwiched in between an active matrix substrate and a color filter substrate located so as to be opposed to each other, and plastic beads disposed between the substrates or a columnar resin structure provided on the color filter substrate and the like are used as a spacer, whereby a thickness (a cell gap or a cell thickness) of a liquid crystal layer is maintained.
In recent years, there is such a tendency that improvements in a speed of response and visual properties (a wide angle of field) are strongly requested particularly as a performance of a liquid crystal display used in a TV with big video screen and the like. As a technology satisfying such needs, a MVA type liquid crystal display unit is disclosed (for example, (see pages 1 to 3, 21, and 66 as well as FIG. 44) of Japanese Patent Application Laid-Open No. 11-242225). In such MVA type liquid crystal display unit, projections (those for an alignment control) for controlling pre-tilts of liquid crystal molecules or electrode slits are usually provided on a surface of substrates. For instance, slits are provided on a pixel electrode (ITO; indium tin oxide) of an active matrix substrate, while a projection row is provided on a color filter substrate in Japanese Patent Application Laid-Open No. 11-242225 (see the sixth embodiment and FIG. 44). When pre-tilts are given to vertically aligned liquid crystal molecules by providing these projections or electrode slits on surfaces of the respective substrates, alignment directions of the liquid crystal molecules are divided, field angle characteristics are improved, and in addition, a speed of response in the liquid crystal molecules can be improved. Furthermore, in Japanese Patent Application Laid-Open No. 11-242225, there are disclosed a structure wherein electrode slits are provided on both of a pixel electrode of the active matrix substrate and an electrode of the color filter substrate, and a structure wherein projections are provided on both the substrates, respectively.
On one hand, when a liquid crystal panel is manufactured, a seal resin is applied around a periphery of inner surfaces opposed to two opposed substrates of an active matrix substrate and a color filter substrate, the substrates are bonded to each other to maintain a gap in between the substrates, and further, it is required to charge a liquid crystal inside the seal providing the gap. As a manner for charging a liquid crystal in between substrates, a (vacuum) pouring method is heretofore employed in general. In the pouring method, a liquid crystal cell formed by bonding two substrates with a seal is maintained in vacuum in a vacuum chamber, air in the liquid crystal cell is excluded, then, the interior of the chamber is returned to normal pressures in a state where an inlet provided on a part of the seal in the liquid crystal cell is immersed into a container in which a liquid crystal is stored, thereby spreading the liquid crystal into the liquid crystal cell, and thereafter, the inlet is sealed with a resin to charge the liquid crystal into the liquid crystal cell.
In such pouring method, however, a period of time for pouring a liquid crystal is prolonged in case of manufacturing a jumboized liquid crystal panel used in a TV with big video screen and the like. For this reason, such a technology that a sealing resin (sealing agent) disposed on a surface of either substrate of two substrates in a rectangular-shaped frame or the like, a liquid crystal is dropped inside of the frame, the resulting substrate is bonded to the other substrate, and the sealing resin is solidified has been developed (for example, see Japanese Patent Publication No. 8-20627 (page 1)). Such method for charging a liquid crystal as mentioned above is called generally “(liquid crystal) drop filling method” in order to discriminate it from a “pouring method”, and accordingly, the former method is getting a very important technology in manufacturing a liquid crystal panel with big video screen.
The above-mentioned MVA type liquid crystal display unit is suitably used for a TV with big video screen. In this connection, when the MVA type liquid crystal display unit is manufactured in accordance with drop filling method, its producibility can be improved. In case of the MVA type liquid crystal display unit, however, there are a vertical alignment film and projections for controlling an alignment, so that a flow resistance of a liquid crystal becomes higher in the vicinities of the alignment film than that of an alignment film for a TN (twisted nematic) type liquid crystal unit, and further, the projections for alignment control become a barrier with respect to fluid flow of the liquid crystal. Moreover, a vertical alignment type liquid crystal used in the MVA type liquid crystal display unit has usually a higher viscosity than that of the TN type liquid crystal. For this reason, when drop filling method is applied, a generation of vacuum air bubbles (remaining air bubbles) due to insufficient extension of the liquid crystal is more remarkably observed in the MVA type liquid crystal display unit than that of the TN type liquid crystal display unit. In this respect, there is room for improvement in filling method with respect to the MVA type liquid crystal display unit.
Some kinds of technology are disclosed as countermeasures for air bubbles in one drop filling method (for example, see Japanese Patent Application Laid-Open No. 2002-107740 (page 1), Japanese Patent Application Laid-Open No. 11-174477 (page 1), and Japanese Patent Application Laid-Open No. 2001-66615 (page 1). However, JP-A No. 2002-107740 relates to a technology for preventing a generation of remaining air bubbles due to an insufficient amount of a liquid crystal, and further, JP-A Nos. 11-174477 and 2001-66615 relate to a technology for preventing a generation of remaining air bubbles due to production of a gas from a color filter substrate. Any of the above-described technologies does not relate to that for improving extension of a liquid crystal.